Hydrogenation of carbon-carbon multiple bonds in the liquid phase



Oct. 22, 1968 F. BECK ET AL 3,407,227

HYDROGENATION 0F CARBON-CARBON MULTIPLE BOND IN THE LIQUID PHASE Filed May 6, 1964 2 Sheets-Sheet l w WWW %Z Oct. 22, 1968 BECK ET AL 3,407,227

F. HYDROGENATION OF CARBON-CARBON MULTIPLE BONDS IN THE LIQUID PHASE Filed May 6, 1964 2 Sheets-Sheet 2 I V) I 5 I I I I Q I *3 l l I' w I -m .g

I I I II o E 1% I A I I I. I I) III) I fi I I I I I I 0 'm I I I I I2 I MS I I I I I I ID I I I I I I I o o o o c') o 0 E I I i HI 1 2 I M/VE/VTORS'. M 3 FR/TZ BECK I LUDW/G SCHUS 7E1? I 3,407,227 HYDROGENATION F CARBON-CARBON MULTI- PLE BONDS IN THELIQUID PHASE Fritz Beck and Ludwig Schuster, Ludwigshafen (Rhine), Germany, assignors to Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany Filed May 6, 1964, Ser. No. 365,465 Claims priority, application Germany, May 10, 1963, Y B 71,842 4 Claims. (Cl. 260-537) ABSTRACT on THE DISCLOSURE Hydrogenation of organic compounds having at least one olefinic or acetylenic bond in liquid phase in presence of suspension of finely divided hydrogenation catalysts, and determining end point of hydrogenation by measuring electrochemical hydrogen reference potentialwith respect to time when change in reference potential reaches maximum value at prevailing pH.

This invention relates to the hydrogenation of carboncarbon multiple bonds in organic compounds. More specifically the invention relates to a new method of determining the end point of such hydrogenations.

Hydrogenation of carbon-carbon multiple bonds in organic compounds, by prior art methods, is carried out in the liquid phase using metals of group VIII of the periodic chart of the elements as catalysts. Determination of the end point of the'hydrogenation, which is particularly important in the selective hydrogenation of triple bonds to double bonds, is effected either by continuously measuring the changes in volume or pressure or, when using flowing hydrogen, by contraction which is defined liters of feed gas-liters of ends gas 00 liters of feed gas or by continuous sampling and analysis.

All these methodshave the disadvantage that the end point of the hydrogenation cannot be determined until some considerable time after it has in fact been reached. Where multiple bonds are being hydrogenated to single bonds, this is not harmful in the ordinary case, but at any rate means a waste of time and often results in waste of energy because the shaking or stirring equipment and the heating or cooling plant continue in operation when it is no longer necessary. In the selective hydrogenation of triple bonds to double bonds any hydrogenating treatment continued beyond the end point of the hydrogenation is always attended by loss of compounds having olefinic double bonds, i.e. with a drop in selectivity. It has therefore become the practice 'to carry out this selective hydrogenations in the presence of poisoned, i.e. less active, catalysts.

It is an object of this invention to improve the prior art process for the hydrogenation of organic compounds having acetylenic triple bonds and/or olefinic double bonds. It is another object of the invention to provide a process for the hydrogenation of the said compounds in which the hydrogenation can be stopped at exactly the time at which one of the olefinic double bonds or acetylenic triple bonds has been hydrogenated. It is a further object of the invention to provide a process for the hydrogenation of the said compounds inflwhich overhydrogenation of the compounds and losses of 'the'desired partly hydrogenated products are avoided. It is finally an object of the invention to provide improvements in the wellknown hydrogenation process, by which waste of energy 3,407,227 Patented Oct. 22, 1968 for stirring, heating or cooling is possible.

The objects and advantages of the present invention will be better understood from the following description in conjunction with FIGURES 1 to 6 of the accompanying drawing.

In the drawings:

FIGURE 1 is a diagrammatic view of electrodes and instrumentation for measuring reference potential;

FIGURE 2 comprises graphs indicating typical reference potential curves A and rate of hydrogenation curves B; and

FIGURES 3-6 comprise graphs of the catalyst reference potential towards the end of their reaction of the last four experiments, respectively, in Table 1, infra, with a gold measuring electrode C and a silver measuring electrode D.

According to the present invention the said objects and advantages in the hydrogenation of organic compounds having carbon-carbon multiple bonds, in the liquid phase containing protons, by contacting said organic compounds with elementary hydrogen in the presence of a catalyst consisting of a suspended finely divided metal are achieved by measuring during hydrogenation the electrochemical hydrogen reference potential at the catalyst and stopping the hydrogenation when the variation in the reference potential with respect to time reaches a maximum value at the prevailing pH value or when it approaches this maximum value.

The maximum value in the variation of the hydrogen reference potential with respect to time constitutes a well definable, hitherto unknown magnitude for the end point of the hydrogenation which can be measured very accuavoided as far as rately in relation to time.

Hydrogenation of the carbon-carbon multiple bonds, i.e. triple bonds and double bonds, is carried out by conventional methods, as described, for example, in Houben- Weyl Methoden der Organischen Chemie, 4th edition, volume 4/2 pages 283 to 295.

Hydrogenation is accordingly carried out continuously or batchwise, for example in a shaking apparatus, by forcing in hydrogen, or in liquid phase while passing through elementary hydrogen which may be used pure or mixed with inert gases, for example nitrogen or rare gases, such as argon. The catalysts are finely or colloidall'y dispersed in the solutions to be hydrogenated.

Examples of suitable unsaturated compounds are aralkyl compounds having acetylenic side chains, particularly those having a benzene radical and one to three side chains each having a triple bond, the side chains containing from two to six carbon atoms; cyclic monoor polyunsaturated hydrocarbons, particularly cycloolefins and cyclodiolefins with five to twelve carbon atoms; olefin and acetylene alcohols, particularly acetylene alcohols (hydroxyalkines) with three to sixteen carbon atoms, one to two triple bonds and one to two hydroxy groups; olefine alcohols (hydroxydiolefins and hydroxytriolefins) with three to sixteen carbon atoms, two to three double bonds and one to two hydroxy groups; esters of these acetylene or olefin alcohols with lower fatty acids with 1 to 4 carbon atoms; vinyl esters; olefinically and acetylenically unsaturated carboxylic acids, particularly acetylene carboxylic acids with one to two acid groups and three or four to ten carbon atoms; and olefine carboxylic acids with one to three double bonds, one to two carboxylic groups and three to twelve carbon atoms; the derivatives of these acids, for example esters of lower alcohols with one to four carbon atoms in each alkyl; unsaturated ketones particularly alkylalkenyl ketones and alkylalkinyl ketones with one to six carbon atoms in the alkyl and two to six carbon atoms in the alkenyl or alkinyl radical.

methylethinyl ketone (acetylaeetylene), and farnesylacetone.

Examples of catalysts for use in the practice of the present invention are: precious metals, particularly platinum, palladium, iridium and ruthenium, and also nickel, cobalt, iron, but also copper. The catalysts may also contain additives which increase or decrease their activity, for example zinc acetate, lead acetate, pyridine, ammonia or triethanolamine. The catalysts may also be used supported or unsupported. Examples of conventional catalysts of this kind are: platinum black, palladium black, platinum on barium sulfate, on graphite or on asbestos, palladium on animal charcoal, on aluminum oxide, on calcium carbonate, on barium sulfate or on silicon dioxide, colloidal platinum, colloidal palladium, platinum oxide, palladium oxide, Raney nickel, Raney cobalt, Raney iron, nickel on diatomaceous earth or pumice.

The catalysts preferred for the hydrogenation of triple bonds to double bonds are: 0.2 to 5% by weight of palladium on silicon dioxide, on aluminum oxide or on calcium carbonate which catalyst may be poisoned by an addition of up to by weight of zinc, e.-g. in the form of zinc acetate; Raney nickel and 1% by weight of platinum on graphite, the percentages by weight being referred to the sum of the catalyst, the carrier, and the catalyst poison, if any. The catalysts are usually applied in amounts of about 1 to 10% by weight with reference to the substrate to the hydrogenated. In some cases, e.g. if the substrate is very dilute in the solvent, even higher amounts, e.g. up to 20% are applied.

The preferred solvent is water to which an electrolyte in the form of salts, acids or bases may be added or a mixture of water with organic solvents miscible with water. Non-aqueous polar solvents may also be used, for example alcohols, particularly those having one to four carbon atoms; ketones, lower fatty acids having two to six carbon atoms and cyclic ethers, particularly methanol, ethanol, n-propanol, isopropanol, acetone, glacial acetic acid, propionic acid, tetrahydrofuran and dioxane, and mixtures of these solvents with water. The concentration of the solutions may vary within a wide range; it is preferable to use 10 to 50% by weight solutions. In the usual case, the salts, acids and/or bases are added in no larger amounts than 2% by weight with reference to the solvent and the substrate to be hydrogenated; larger amounts, :while not harmful, do not offer any advantage. Examples of such additions are lower alkane carboxylic acids, mineral acids, alkanolamines, aliphatic amines, ammonia, sodium sulfate, sodium perchlorate and lithium nitrate. Preferred compounds are acetic acid, sulfuric acid, triethanolamine and/or ammonia used in an amount of 0.1 to 2.0% by weight. If the substrate itself is a polar liquid, as in the case, for example, of dimethylethinyl carbinol, it may be processed either in .a state of high concentration or in the absence of any solvent. In this case also the said additives may be advantageous. It should be noted that the pH of the solution to be hydrogenated is not critical; however the hydrogen reference potential changes with the pH and therefore, in a preferred embodiment of the present invention, provision is made that no change of the pH during reaction occurs, e.g. by the addition of buffer substances; however if a change of the pH during reaction occurs the change of the hydrogen reference potential can be calculated from this change of the pH and taken into account in the change of the hydrogen reference potential as a result of the completion of the hydrogenation reaction.

The measuring instrument used for the indication of the catalyst reference potential (valve voltmeters or voltage recorders) should have an impact resistance which is greater than the internal resistance of the system. This requirement is easy to fulfill because a large selection of equipment is commercially available which has an impact resistance of 10 ohms or more and is suitable for pH measurements with glass electrodes. When using Water or mixtures of water with polar organic solvents, the specific conductivity is of the order of magnitude of 10- to 10* Siemens per cm., and this is adequate for measurements with this equipment. Here again, an addition of an electrolyte is advantageous to ensure steadiness and reliability in the control of the reference potential. Preferred electrolytes are those, i.e. functioning to stabilize the pH value, having buffer action as for example arnmonia or amines and their salts, carboxylic acids and their salts or strong acids. However, the method is also practicable if the pH value in the solution shows a constant course during the hydrogenation reaction, because this becomes evident only in a corresponding course in the catalyst reference potential, while it leaves the marked variation in this measurement quantity at the end point of the hydrogenation reaction unaffected.

The catalyst is used in a finely suspended condition. The volume ratio of the catalyst to the compound to be hydrogenated and the concentration of this compound in the solvent used, are within the limits set by prior art standards. They are to be correlated to the catalyst and substrate to be hydrogenated.

The hydrogenation process is carried out within conventional temperature and pressure ranges. For example the hydrogenation of triple bonds to double bonds or of diolefines to monoolefines is carried out at a temperature of between 0 and C., particularly 20 and 60 C., and at a total pressure of from atmospheric pressure up to about 15 atmospheric pressure, preferably up to 8 atmospheres gauge. The conditions most favorable for various substrates to be hydrogenated are known. Thus, for example, butindiol is hydrogenated with advantage in a from 2 to 33 percent-by-weight solution in water, to which buffer substances, as for example an amine or acetate buffer, or sulfuric acid (in an amount of from 0.1 to 0.2 percent by weight) may be added, at a temperature of between 25 and 60 C. and at a pressure of from 1 to 9 atm. abs., in the presence of a supported palladium catalyst, with or without an addition of from 1 to 10 percent by Weight of zinc ions as a catalyst, percentage with reference to the catalyst. Tetramethylbutindiol can be hydrogenated at a temperature of between 25 and 50 C. and at a pressure of from 1 to 10 atm. abs. using solutions which contain from 5 to 50 percent by weight of methanol and may contain a small amount of sulfuric acid and working in the presence of supported palladium as a catalyst. Dimethylethinyl carbinol can be hydrogenated with very good results in from 8 to 88 percent solutions in water or alcohols with up to 4 carbon atoms to which an amine buffer may be added, while using calcium carbonate or silicon dioxide supported palladium or Raney nickel as a catalyst. The hydrogenation of cyclooctadiene to cyclooctene is advantageously carried out in from 5 to 20 percent by weight solutions in alcohols with up to 4 carbon atoms to which sulfuric acid and/or an acetate buffer may be added, at a temperature of between 25 and 40 C. and at a pressure of from 1 to 9 atm. -abs., in the presence of supported palladium as a catalyst. The foregoing examples are given for illustration only without any intention to restrict our invention to the specific data indicated.

The reference'potential is measured by conventional means, for example with a measuring equipment as shown diagrammatically in FIGURE 1 of the accompanying drawing. A measuring electrode 1 is connected in an appropriate way with a reference electrode 2 and the voltage ismeasured with a conventional instrument 3 or continuously recorded. To provide satisfactory potential conditions at the measuring electrode it is advantageous for the catalystsuspension to flow directly against it. During reaction a stationary state of the supply of molecular hydrogen to the surface of the catalyst should be set up by suitable stirring and dispersion of hydrogen in the solution, because variations in the rate of this supply may result in marked variations inthe catalyst reference potential. The measuring electrodes are usually gold or silver electrodes. They should not be of the same material as the catalyst. Calomel. (mercurous chloride) or silver/ silver chloride electrodes are usually employed as the reference electrodes. The measuring instrument 3 should be adapted to the electrodesused and also to the resistance in the measuring circuit.

The typical course of a reference potential curve during hydrogenation, for example, of 2-butinediol-(1,4), in the presence of aluminum oxide supported palladium catalyst is shown in curve A of FIGURE 2 of the accompanying drawing, together with the course of the rate of hydrogenation. In FIGURE 2, curve B reproduces the course in time of the reference potential and the rate of hydrogenation in the hydrogenation of dimethylethinyl carbinol in contact with a silicon dioxide supported palladium catalyst. a marks the beginning of the hydrogenation, 11 marks the end of the hydrogenation of the triple bonds and c marks the end of the hydrogenation of the double bonds. In both cases the CEC- bonds have been partly hydrogenated to the -C=C bond stage at the pointin time b and this is made evident by a marked displacement of the reference potential in negative direction.

The process gives particularly favorable results in the selective hydrogenation of triple bonds to olefinic double bonds and in the selective hydrogenation of compounds having a plurality of unsaturated bonds of different reactivity. The hydrogenation may be'stopped with very high precision when the first stage of the hydrogenation comes to an end.'Moreover,' these selective hydrogenations maybe" carried out even with very active (unpoisoned) catalysts, if the substance to be hydrogenated is adsorbed so firmly'on the catalyst that any further hydrogenation of the carbon-carbori double bond is inhibited during the first stage. This is the case, for example, when the compound to be hydrogenated contains'a carbon-carbon triple bond. In this case, however, it is particularly important to know exactly at what time to stop the reaction because the said inhibition ceases after disappearance of the -CEC-- bond and the hydrogenation of the C=C- bond sets in with comparable speed. For'this purpose the electrochemical measuring method referred to above canbe used to special advantage, even in cases in which the rate of hydrogenation changes only a littleor not at all after the first stage.

The following examples will further illustrate the invention.

Example 1 4.5 g. of a palladium catalyst poisoned with zinc (5% of Pd on gamma-Al O -I-3% of zinc acetate) in 500 ml,

of water to "which 7.5 g. of'triethanolamine and 1.5 g. of acetic acidhave been added is placed in a 1 liter glass fiask fitted with a 35 mm. gate paddle agitator, a measuring electrode (gold or silver), an electrolyte siphon for minutes; this. ismade, evident bya constant hydrogen equilibrium reference potential of 678 mv. being set up (the reference potential, as in all following occurrences, is measured against a saturated calomel electrode). When 10.56 g. of 2-butinediol-(1,4) is added in the form of a concentrated aqueous solution, the catalyst reference potential is displaced in a positive direction within a few seconds. A value of 540 mv. is set up which steadily declines in the course of 3.5 hours to 570 mv., when a more marked variation begins reaching its maximum after 4 hours and 10 minutes (AU/At=10 mv./min. at -630 mv.)

At this time, one equimolar amount of hydrogen .has

been absorbed, i.e. the triple bond hasbeen hydrogenated to a double bond.

.Example 2 Using an apparatus as described in Example 1, the catalyst feed stock put in consists of 5 g. of a palladium catalyst (5% Pd on Si0 in 500 ml. of 60% methanol to which 7.5 g. of triethanolamine and 1.5 g. of acetic acid have been added. When 15.4 g. of linalool is added to the system saturated with hydrogen, the catalyst reference potential rises from -680 mv. to about '-300 mv. and then, as the hydrogenation proceeds, falls continuously to -550 mv. within 46 minutes at a temperature of about 40 C., when the reference potential suddenly changes again more markedly reaching its steepest decline after fifty minutes (35 mv./min. at 630 mv.). At this time, one equimolar amount of hydrogen has been absorbed, i.e. the terminal double bond in the molecule has been selectively hydrogenated.

Example 3 Using an apparatus as described in Example 1, the catalyst feed stock put in consists of 5 g. of a palladium catalyst (4% of Pd on SiO in 500 ml. of isopropanol to which 2.5 g. of sulfuric acid has been added. When 54 g. of cyclooctadiene-(1,5) is added to the system saturated with hydrogen (at 40 C. and 600 r.p.m. of the stirrer), the catalyst reference potential rises from -270 mv. to 170 mv. After hydrogenation for one hour at a mean rate of hydrogenation of 178 ml. of H per minute, the reference potential has fallen steadily to 210 mv. The reference potential then drops steeply reaching a maximum value after one hour and ten minutes (5 mv. per minute at 240 mv.) At this time, one equimolar amount of hydrogen has been absorbed, i.e. one of the two double bonds in the molecule has been selectively hydrogenated.

When hydrogenating 16.4 g. of cyclohexene under the same conditions, the catalyst reference potential rises from 270 mv. to 160 mv. when the substrate to be hydrogenated is added. After 43 minutes this value has steadily fallen to 200 mv. The reference potential then begins to change more markedly reaching a maximum value of 11 -mv. after 43.5 minutes. At this time one equimolar amount of hydrogen has been absorbed. The speed of hydrogenation is ml./min. at the beginning and slows down steadily towards the end of the hydrogenation.

Example 4 A 500 ml. glass flask equipped as described in Example 1 is fed with 5 g. of a dry palladium catalyst (0.8% of Pd on SiO and then filled with hydrogen. A solution of 100 g. of 1,1,4,4-tetramethyl-Z-butinediol-(1,4) in ml. of 0.05 N methanolic sulfuric acid is added through the dropping funnel and the hydrogenation reaction is carried out at 40 C. and a speed of the gate paddle-agitator of 600 r.p.m. The catalyst reference potential drops steadily in the course of eight hours from -60 mv. to mv. The course of this measurement value with respect to time then exhibits a sudden drop which reaches a maximum after eight hours and sixteen minutes (about 2 mv. per minute at mv.) At this time, one equimolar amount of hydrogen has been absorbed, i.e. the

'7 CEC- triple bond in the molecule has been selectively hydrogenated to the -C=C double bond.

If the same experiment is repeated with a more dilute mixture of 70 g. of tetramethylbutinediol in 160 ml. of 0.05 N methanolic sulfuric acid, the rate of hydrogenation is more than twice as high, the end point being indicated after two hours and twenty-two minutes by the steepest decline in the reference potential (about 3 mv. per minute at 190 mv.).

Example 5 Using an apparatus as described in Example 4, 15 g. of a dry palladium catalyst (0.8% of Pd on CaCO which has been poisoned with 4.5% of zinc acetate is fed in and the system is filled with hydrogen. A mixture of 214.3 g. of technical-grade dimethylethinyl carbinol and 15 g. of aqueous ammonia solution is added through a dropping funnel. Hydrogenation is then carried out at 60 C., the gate paddle agitator running at a speed of 1500 r.p.m. The catalyst reference potential steadily drops from 600 mv. to 650 mv. in the course of seven hours and fifteen minutes, when a much more marked variation occurs which reaches its maximum value after seven hours and twenty-one minutes (11 mv. per minute at 705 mv.). The reaction is stopped at this point in time and the mixture is analyzed by gas chromatography (6 m. K-column, 125 C.). It contains 0.0% of dimethylethinyl carbinol, 98.9% of dimethylvinyl carbinol and 1.1% of dimethylethyl carbinol, percentages with reference to the original content of dimethylethinyl carbinol.

Table 1 hereinafter gives the results of eight hydrogenation experiments carried out with dimethylethinyl carbinol under different conditions. In each experiment the reaction is stopped when the drop in the reference potential is at its steepest, and the reaction mixture is then analyzed by gas chromatography. Of any two experiments one has been carried out with a conventional and one with a zinc-poisoned palladium catalyst. It will be seen that the selectivity is about equally good in either case, but the rate of hydrogenation, as would be expected, is much higher with the unpoisoned catalyst. FIGURES 3 to 6 of the accompanying drawing indicate the course of the catalyst. reference potential towards the end of the reaction for the last four experiments in Table 1. In each case, curve C relates to the use of a gold measuring electrode and curve D to the use of a silver measuring electrode. Point E indicates stoppage of the reaction.

pressure-tight manner. A millivolt recorder registers the course of the voltage.

In each case 17.35 kg. of technical-grade 1,4-butinediol solution (33 is charged into the autoclave and adjusted to a pH of 7.5 with concentrated ammonia solution. After adding 1.5 kg. of catalyst (0.2% of Pd on gamma-A1 0 plus 2 to 3% of Zn), the autoclave is flushed with nitrogen and hydrogen and then hydrogen is forced in until the pressure given in Table 2 hereinafter has been set up. Absorption of hydrogen begins immediately after the agitator is switched on. The temperature rises from about 20 to C. and is kept at the latter level by external cooling. The voltage in' the chain of electrodes rises suddenly to a definite level at which it remains practically constant until the triple bond has been saturated to a double bond. Shortly prior to this, the voltage rises further, at first slowly and then more and more rapidly. The most favorable point at which to stop the hydrogenation can be seen from the curve. It is advantageous to effect the stoppage at the instant where the change of voltage is at its maximum.

For analysis a small portion of the solution is suction filtered from the catalyst and freed from water in vacuo. The residue is investigated by gas chromatography. The

percentages are area percentages.

- TABLE 2 Example No 6 7 8 9 Temperature in C 45 45 60 Pressure in atmospheres gen 5 8 6 6 Absorption of H2 in liters. 1, 750 1, 845 2,140 2, 500 Duration in minutes 115 110 Minimum mV 503 546 525 512 Maximum mV 552 605 584 553 Ultimate mV per minute. 10 33 20 12 Composition of the residue Butinediol Butenediol 100 100 100 Butanediol Yield in percent of the theory 97 96. 5 96.0 96. 5

Example 10 A suspension of a calcium carbonate supported palladium catalyst which contains 0.8% of palladium and has been poisoned with 5% of zinc acetate, in 500 ml. of methanol, to which 5.4 g. of triethanolamine and 1.5 g. of acetic acid have been added, is placed in an apparatus described in Example 1. After adding 46.5 g. of phenylacetylene to the hydrogen-saturated system of 35 C. and a rate of agitation of 650 rpm. the catalyst reference po- TABLE I.SELEC'IIVE IIYDROGENATION OF DIMETIIYLE'IHINYL CARBINOL UNDER DIFFE RENT CONDITIONS Experiment No 1 2 3 4 5 6 7 8 Temperature, 0. 25 25 25 no 60 e0 60 Speed otstirrer (rnin.- 000 000 1,200 1,000 1,000 1,500 1,500 Composition of the reaction are n percent by w glit, dimethylethinyl carbinol 7. 7 0. 4 0. 3 l 47. 0 1 47. 0 1 S7. 7 l 87. 7 \Vater 87.4 5 5 Methanol 84. 6 83. 7

Isoproptmol Triethnnolamiue buffer pH 8 4.0 4. 9 4.8 Ammonia Catalystt 0.9 1. 8 1. 1 2. 2 Catalyst used:

Percent of Pd 4 4. 5 4 4, .3 gflIl'lel d ti;.7- CiKiO; Sign CaCO; SiOi oisone wt .ln 'es 0 Ye Mean rate 01 hydrogenation in first stage (with reference to 1 kg. of res No Yes Yes 0 action mixture) in ml. Iii/min. kg 100 440 1,010 327 560 690 l 030 Composition alter hydrogenation (with reference to substrate):

Dimethylvinyl carbinol (in perccnt). 87 96 01 0t 98. 2 98. 7 98. 0 97. 2 Dlmethylethyl carbinol (in percent) 12.2 3.8 8. 0 5.0 1. S 1. 25 1. 2. 8

1 Technical grade.

Examples 6 to 9 Hydrogenations are carried out in a 35 liter stainless steel autoclave. The vessel is fitted with a high speed gate paddle agitator for intense mixing of the liquid phase with the gaseous phase.

An electrode of gold foil, connected to a calomel electrode, is used for measuring the electrochemical hydrogen reference potential at the powder-form catalyst. The two tential rises from 674 to 430 mv. This value hardly changes in the course of 50 minutes at a mean rate of hydrogenation of ml./min. Then the reference potential begins to drop sharply attaining a maximum value of 100 mv. after 52.5 minutes, when one equimolar amount of hydrogen has been absorbed.

If the experiment is repeated with a different catalyst, i.e. 10 g. of Raney nickel, the catalyst reference potential,

electrodes are passed through the autoclave cover in a 75 after the substrate to be hydrogenated has been added,

rises from 663 to --600 mv. After 80 minutes a marked change of the reference potential becomes evident reaching a maximum value of 17 mv./min. after 84.5 minutes. At this time one equimolar amount of hydrogen has been absorbed. The rate of hydrogenation is 220 rnl./ min. at the beginning and 110 mL/min. after 80 minutes.

Example 11 A suspension of g. a 0.8% silicon dioxide supported palladium catalyst in 500 ml. of methanol, to which 3.5 g. of acetic acid and 1.5 g. of sodium acetate have been added, is placed in an apparatus described in Example 1. After adding g. of acetylacetylene to the hydrogensaturated system at C. and at a rate of agitation of 650 r.p.m., the catalyst reference potential rises from 618 to -525 mv. This value has hardly changed after 170 minutes, being then -520 mv. when a marked change in the positive direction begins attaining a maximum value of mv. after 182 minutes. At this time one equi. molar amount of hydrogen has been absorbed. The rate of hydrogenation is 28 mL/min. at the start and 84 ml./ min. at the end.

Example 12 A suspension of 5 g. of a 4.5% silicon dioxide supported palladium catalyst in 500 ml. of acetic acid, to which 20 g. of sodium acetate have been added, is placed in an apparatus as described in Example 1. After adding 25 g. of farnesylacetone having the formula to the hydrogen-saturated system at 25 C. and a rate of agitation of 600 r.p.m., the catalyst reference potential measured by means of a silver probe, rises from -336 mv. to --282 mv. After minutes the value has steadily changed to a level of -300 mv. The mean rate of hydrogenation is 20 ml./ min. The hydrogenation then begins to slow down steadily and at the same time the catalyst reference potential changes more rapidly attaining a maximum value of 2 mv./min. after minutes, when one equimolar amount of hydrogen has been absorbed.

10 Example 13 A suspension of 12 g. of a 5% aluminum oxide supported palladium catalyst in 500 ml. of water, to which 1.5 g. of sulfuric acid of 100% strength have been added, is placed in an apparatus described in Example 1. After adding 16.1 g. of acetylene dicarboxylic acid to the hydrogensaturated system at 40 C. and a rate of agitation of 650 r.p.m., the catalyst reference potential rises from 394 to mv. It is mv. after 120 minutes and then begins to change more markedly attaining a maximum value of 40 mv./min. after 136 minutes, when one equi molar amount of hydrogen has been absorbed. The rate of hydrogenation is 20 ml./min. at the start and 28 ml./ min. near the end point.

We claim:

1. A process for the hydrogenation of organic compounds having at least one olefinic or acetylenic bond which comprises contacting said organic compounds while in liquid phase, with hydrogen in elementary form, in the presence of a suspension form finely divided metallic hydrogenation catalyst, measuring the electrochemical hydrogen reference potential during hydrogenation and stopping the hydrogenation when the change in the reference potential with respect to time reaches a maximum value at the prevailing pH.

2. A process as claimed in claim 1 in which an acetylenic compound is hydrogenated to an olefinic compound.

3. A process as claimed in claim 1 in which a compound having a plurality of double bonds is partially hydrogenated.

4. A process as claimed in claim 1 wherein a temperature of between 0 and 100 C. and a pressure of from 1 to 15 atm. absolute is used.

References Cited Houben-Weyl, Methoden der Organischen Chemie, 4th edition, vol. 4/2, pages 283-295.

LORRAINE A. WEINBERGER, Primary Examiner. V1. GARNER, Assistant Examiner. 

